The present invention relates generally to a solar panel for heating the water of a swimming pool or spa, although the invention is not so limited. Some conventional solar panels of this type are generally referred to as being of “mat” or “web” construction or type, because they include a generally flat or blanket-like mat or web of plural relatively small, elongate parallel tubes or conduits. These small tubes of the mat are united by a diaphragm or web of material, and serve as solar heating collectors. As explained, the plurality of small tubes may be united into a unity or into groups, in side-by-side parallel array by a comparatively thin web of material. Further, the web or mat of plural small tubes are terminated at each of their opposite ends in water flow communication with a respective one of a pair of larger manifold conduits. The pair of larger manifold conduits generally extend perpendicularly to the small solar collector tubes of the mat. Particularly, such low-pressure, water-heating solar panels of this type are used to circulate water from a pool or spa under relatively low pressure (perhaps provided by a pool pump, or by a solar heating pump—which may be line powered or even may be powered by solar electric panels) in heat absorbing relation with solar radiation (i.e., the solar panel is exposed to the sun). For this purpose, such solar panels are generally installed adjacent to, or on the a roof perhaps, of a residence or other building having an associated pool which it is desired to heat. By the use of such solar pool and spa heating, the use of natural gas and other fossil fuels for pool and spa heating is eliminated or greatly reduced. Also, the swimming season for the pool and/or spa is greatly extended in both the spring and the fall in areas where such a pool or spa may otherwise be usable (with comfortably warm water temperatures) only during a comparatively short mid-summer part of each year.
Conventional low-pressure solar panels of this type include the mat structure of plural relatively small parallel tubes or conduits, and respective opposite manifold tubes or conduits of a size considerably larger than the mat tubes. During manufacture of such mat type solar panels, a number of alternative manufacturing expedients may be utilized. One such manufacturing expedient is to extrude the tubes of the mat, along with an interconnecting web or diaphragm, as a long extrudate (i.e., an elongate article made by extrusion of molten plastic through a profiled die followed by cooling of the plastic) provided in rolls for installation. The manifold tubes are then provided with a parallel plurality of outwardly projecting hose barbs or nipples, to which the mat is connected after being cut to the desired length. That is, each of the plural small tubes of the mat are individually fitted over a respective hose barb or nipple at the manifolds in order to connect the manifolds and mat. This fitting job is generally done by an installation technician, who also completes the remainder of the solar panel installation. This version of mat type solar panel is very labor intensive to install, although it has found some favor with certain “do it yourself” home owners.
Another form of such a mat configuration of low-pressure water-heating solar panel takes the form of a mat of plural tubes which is either solvent welded, or ultrasonically welded, or over-cast permanently into flow communication with a pair of manifold tubes.
In each of the conventional mat type of low-pressure, water-heating solar panels discussed above, the mat of plural tubes intersects the manifold tubes in alignment with the longitudinal axis of the manifold tubes. As will be seen, this construction has a serious disadvantage, especially in parts of the country where freezing temperatures are experienced during winter.
Consideration of how such mat type of low-pressure, water-heating solar panels are installed and used will reveal that such panels are generally held on a frame, perhaps mounted to a roof, and have the manifold tubes disposed generally horizontally, with the plural tubes of the mat extending generally vertically. In this orientation, low-pressure water from a pool or spa is pumped to the panel along one of the manifold tubes, flows along the plural relatively small tubes of the mat in heat absorbing relation with sun light, and is collected at the other manifold tube. During warm weather conditions, this scheme of operation works well. However, in areas which experience freezing temperatures, the solar panel must be drained in order to prevent freezing water within the panel from destroying the panel structure. To this end, many solar panel installations include a vacuum breaker valve which is temperature responsive so as to open and allow draining of water from within the solar panel in the event the ambient temperature drops close to freezing, to about 34° F., for example. In this way, it is sought to safeguard the solar panel from damage by water freezing within the panel. As will be seen, these efforts are somewhat ineffective with conventional solar panel designs.
A common problem resulting from the imperfect design of conventional solar panels of the type discussed above is that not all water is able to drain from the panel. That is, a puddle of water remains in the panel after draining, and may freeze to damage the solar panel. Such is the case because water may be trapped in one of both of the manifold tubes, and be unable to drain from the panel.
Turning now to consideration of the appended drawing Figure indicated as “prior art,” (i.e., FIG. 8) it will be understood by those ordinarily skilled in the pertinent arts that a conventional mat type of solar panel 10 is generally of rectangular or rectilinear shape in plan view (the plan view not being seen in FIG. 8—but being similar to that seen in diagrammatic FIG. 1), and is attached in an angled orientation to a support surface, which may be provided by a support rack or roof, generally indicated with the numeral 12. This angulated orientation of the conventional solar panel both improves the presentation of the solar panel absorbing area to the sun, and is thought to effect draining of the solar panel when it is desired to protect the panel from freezing conditions. Consideration of the construction of the conventional solar panel 10 (seen in side elevation cross sectional view in FIG. 8) will show that it includes an elongate “mat” or “web” section 14 consisting of plural side-by-side relatively small solar collector tubes 16 (only the closest one of these tubes being visible to the viewer of the “prior art” FIG. 7, as this Figure is seen in cross section of a side elevation view). The tubes 16 are generally formed as part of an elongate plastic or polymer extrudate, including a relatively thin interconnecting web or diaphragm portion, indicated with the numeral 18. At the upper and lower ends of the mat 14, the plural tubes 16 are each connected in flow communication with a respective manifold tube 20, 22 (i.e., with flow passages 20a and 22a, respectively) of a size considerably larger than the small tubes of the mat 14. The small tubes 16 and the manifold tubes 20, 22 intersect or interconnect along lines intersecting the centerlines of the small tubes 16 and the centerlines of the larger manifold tubes 20, 22.
Consequently, when the solar panel 10 is supported on a flat (and perhaps angled as shown) surface, then the mat 14 of the solar panel 10 spans between the manifold tubes 20, 22 above the surface 12, defining a gap, indicated with the numeral 24. Actually, because the mat 14 is made of a somewhat flexible plastic material, this mat may sag somewhat between the manifold tubes 20 and 22, so that over a central part of its length it is somewhat slack and rests upon the surface 12, except adjacent to the manifold tubes 20 and 22. This flexibility, slack, and sagging of the conventional solar panels has another undesired result, which is further explained below. Consequently, as is seen in the upper part of the “prior art” Figure, when the solar panel 10 is drained, a puddle of water still remains in the upper manifold tube 20. This puddle of water may be sufficient that water not drained from the solar panel intrudes into fissures and cracks of the solar panel structure. Perhaps these fissures and cracks would not otherwise cause a problem, but over time as these fissures and cracks of the solar panel are widened and weakened by repeated cycles of water freezing and expanding in them, they can lead to leaks of the solar panel. In fact, such leaks of this type of solar panel in areas experiencing freezing temperatures are a leading cause of warranty claims, customer dissatisfaction, and complaints against this type of solar panel.
As can be seen, there is a need for an improved low-pressure, water-heating solar panel that will drain completely so as not to retain water that may freeze within the panel.
Also, there is a need for an improved low-pressure, water-heating solar panel that may more easily be installed on a rack or on a roof, for example, in order to better support the solar panel and to protect it from severe weather conditions, such as high winds. As can be seen from the “prior art” FIG. 8, conventional solar panels of this type inherently do not fit closely to the rack or roof surface on which they are mounted (i.e., recalling gap 24), and have an additional undesired consequence or disadvantage, which was alluded to above. This disadvantage results from the slack and flexible nature of the solar panel combined with the possibility of wind getting under the panel via gap 24. The gap 24, combined with the slack in and flexibility of the solar panel web presents an opportunity for high winds to lift the web portion of the solar panel. Once the web portion of such a conventional solar panel is lifted by strong winds the solar panel may flap uncontrollably like a flag in a stiff breeze, and the chances of the panel being damaged or destroyed are very great.